It's not hard to see why Boom sold poorly. Sonic Boom: Shattered Crystal ended up with a Metacritic rating of 47, while Rise of Lyric is sitting at an impressive 33. Here are some choice quotes from reviews:

"One thing I’m sure of is that Sega ought to be embarrassed for pouring so much hype, so much marketing money, into this project, only to have a sad, miserable little dog’s dinner of a product to show for it. I guess it doesn’t matter, though. It’s an idiotic baby’s game for children, and it exists to sell toys. It also thinks you’re all dumb, and it wears its contempt for you on its sleeve. A sleeve covered in bandages." - Jimquisition

"Sonic Boom: Rise of Lyric is simply a disaster. To my knowledge, it is the worst retail game I have played in a long time. The game is boring, chock full of problems and glitches, and doesn't know when to be quiet for even a moment. Even it was meant as a game for children, I consider it an insult for the age demographic." - NWR

"The time is clearly long overdue for Sonic to take a well-earned rest, get his breath back and only return once Sega has worked out where he's supposed to be going. It pains me to say it, but Sonic Boom needs to be the last noise we hear from the blue hedgehog for a very long time." - Eurogamer

"One of the 16-bit era’s most famous game franchises is now of a lower priority to Sega than getting their new Sonic Boom lunchbox and cuddly toys to shop shelves on time. The mighty have not only fallen they have, like so many hedgehogs before them, become nothing but a flattened corpse by the roadside." - Metro

It's hard to imagine that Sonic could actually sink any lower. Sonic, once the face of Sega and a series capable of selling consoles on its own merit, hasn't been worth gamers' attention for a long time. The franchise has been in a sorry state for years thanks to a long chain of throwaway titles like Sonic and the Black Knight, Sonic Riders and many others I've tried to forget. You know your franchise is in trouble when the kart-racing spin-offs are leagues better than the main series.

What makes the failure of the Sonic Boom games even sadder is that they might be the last console installments of the series. Sega recently laid off hundreds of employees and announced that they're going to focus on PC and mobile games.